Many different types of cooling systems presently exist, such as systems operating a thermal transfer cycle to remove heat from one heat sink region and transfer this heat to a different heat sink region, including reverse cycle heat pumps and vapor-compression refrigeration systems such as air conditioners, refrigerators, freezers and water chillers. Water heating is known to be accomplished by resistive heating, burning of fuel, chemical reaction and the like. Some relevant references are the following: U.S. Pat. No. 2,548,508, April 1951 to Wolfner; U.S. Pat. No. 2,893,218, July 1959 to Harnish; U.S. Pat. No. 2,975,609, March 1961 to Allander et al.; U.S. Pat. No. 3,188,829, June 1965 to Siewept et al.; U.S. Pat. No. 3,362,184, January 1968 to Jensen; U.S. Pat. No. 3,976,123, August 1976 to Davies; U.S. Pat. No. 4,089,667, May 1978 to Jonsson; U.S. Pat. No. 4,098,092, July 1978 to Singh; U.S. Pat. No. 4,173,865, November 1979 to Sawyer.
A thermal transfer cycle for cooling may be accomplished by a compressor, condenser, throttling device, and evaporator connected in serial fluid communication with one another in a refrigeration cycle. The system is charged with a refrigerant which circulates through each of the components to remove heat from the evaporator and transfer heat to the condenser. During operation, the compressor compresses the refrigerant from a saturated-vapor state to a super-heated vapor state thereby increasing the temperature, enthalpy, and pressure of the refrigerant. The refrigerant then flows through the condenser which condenses the refrigerant at a substantially constant pressure to a saturated-liquid state. The throttling device reduces the pressure of the refrigerant thereby causing the refrigerant to change to a mixed liquid-vapor state. The refrigerant then flows through the evaporator which causes the refrigerant to return at a constant pressure to its saturated-vapor state thereby completing the thermal transfer cycle. The cycle requires energy to transfer the heat from one location to another.
In refrigeration, it is readily apparent that the condenser plays a major role in the refrigeration cycle, which is a thermal transfer cycle. The most common type of condenser presently in use for domestic systems is commonly referred to as an “air-cooled condenser”. Such air-cooled condensers typically operate by subjecting the condenser to a flow of free air which absorbs the heat being discharged by the condenser. The advantages of such air condensers include the low cost of moving the free air by fans powered by electric motors, the availability of air, and the ease of discharging the heat laden air. The disadvantages of such air condensers is the need for an extremely large heat exchange surface area of the condenser to effect the heat exchanging relationship between the refrigerant passing through the condenser and the flow of free air, the relatively high head pressure involved on the compressor, the fluctuating humidity and temperature of the air, and the lack of any significant subcooling of the liquid refrigerant flowing from the condenser of standard operating conditions. Because of such problems, the air-type condensers are used in conjunction with relatively small refrigeration systems such as those commonly used for domestic purposes.
The second most prevalent type of condenser is what is commonly referred to as a water-cooled condenser in which water is circulated about or through the condenser to absorb the latent heat of condensation of the refrigerant as the refrigerant is condensed within the condenser. The advantages of such water cooled condensers are the fact that the condenser drops the head pressure off the compressor very rapidly, thereby reducing the pressure differential across the compressor. The amount of electric current required to power the compressor is therefore substantially reduced. Moreover, water-cooled condensers cool the refrigerant by as much as 30.degrees. F. over that of an a-cooled condenser. Such subcooling increases the refrigerating effect of the refrigeration cycle by 18 percent to 37 percent or more. Unfortunately, the primary disadvantage of a water cooled condenser is the need for a great volume of water (approximately 2 to 3 gallons per minute per tonnage of cooling capacity as recommended by most manufacturers). Additionally, problems exist in discharging the heated water to the environment. For these reasons, water cooled condensers are typically found only on commercial refrigeration systems having cooling capacities greater than 3 tons (12,000 British Thermal Units per hour) and are subject to government regulation.
In order to reduce the volume of water discharged in a water-cooled condenser, various water tower condensers have been designed. Typical water tower condensers comprise a reservoir of water which is pumped through a water/refrigerant heat exchanger. The water absorbs heat of condensation of the refrigerant. The absorbed heat in the water is then rejected into the atmosphere by evaporation of some of the water, with the heat of vaporization of the water being used to cool the remaining water. It is noted that due to the evaporation of water, a supply of water must be continually fed to the reservoir to maintain the reservoir at a proper water level. The equilibrium water temperature attainable is equal to the ambient wet bulb temperature. This causes similar problems as noted on air-cooled condensers, because as ambient wet bulb temperature increases, the efficiency of the condenser decreases. Cooling towers of this type are highly regulated and require permits for the use of water.